The bump, a manifestation of a shock wave on the descending branch or around minimum, is a very remarkable feature of certain monoperiodic RR Lyrae stars. Excellent theoretical identification, as one of the three shock waves, is given by Fokin et al. [5]. The CoRoT Space telescope supports us with incredibly high precision datasets. They allow us to carry out investigations that have never been possible before. Using a 152-day long CoRoT dataset we are able to divide it not only into shorter subsets (check for short-term variability) but into segments according to the remarkable features of the light curve.

EN2_STAR_MON_0101370131 is a monoperiodic, non-Blazhko CoRoT RR Lyrae star of the first long run with a very definite bump on the lower part of the descending branch. The light curve is nicely fitted by the pulsation period and its 33 harmonics. The harmonics are highly needed to describe the descending branch. A definite question was addressed to the dataset: can we connect certain harmonics to the special features of the light curve? Our result shows that the 4th and 7th harmonics have close connection to the bump. Our observational results are compared to the results of the theoretical light curve selected from a grid of RR Lyrae models. Investigation of a radial dependence of the shock waves' characteristic timescale needs a theoretical model with properly zoned outer layers.